We thank Trevisanuto et al for their comments; their findings on a larger population of very low-birth weight infants, using Shukla and Ferrara’s formula, confirm the need for a new formula to improve the rapid calculation of umbilical arterial catheter insertion distance, as we have suggested. To clarify one point in their response, we actually used lines inserted by the Shukla calculation to devise the new approach, but the randomized trial reported was against a published nomogram, which is probably more widely used worldwide and is based on the original data from Dunn. Thus, the new formula should have validity against all current methods.